1. Field of the Invention
The present invention relates to self-calibration methods for a key-type computer mouse or cursor positioning device which derives its positioning information from pressure sensors. More particularly, the present invention is directed to automatic calibration methods for a force sensitive resistor-based cursor positioning device embedded in a computer keyboard or pointing device.
2. The Prior Art
The development of graphical user interfaces for personal computers has resulted in a demand for cursor positioning devices more versatile than the traditional cursor keys (arrow keys) included in almost all computer keyboards. Mice, joy sticks and track balls have all been adapted for use with personal computers. Yet, all of these devices require that the hand that types on the keyboard be moved away from the keyboard in order to provide input to the computer from the mouse, joy stick or track ball which is often relatively distant from the keys of the keyboard. U.S. Pat. No. 5,124,689 to Franz et al. discloses a cursor control device embedded in a computer keyboard. Four force sensitive resistor grids (FSRs) may be coupled to one of the computer keys, for example, the "J" key. Key contact closures and FSR output values are monitored to determine when the J key is pressed and pushed in a particular direction for use in cursor control as opposed to as a typed "J". Data from the FSRs is processed to direct movement of the cursor displayed on an associated computer display.
The prior art, however, does not take into account the fact that FSR-type sensors are subject to many forces and effects which cause their nominal output values to drift over time. For example, changes in temperature, humidity, atmospheric pressure and position can all cause the output values of an FSR sensor to change regardless of how carefully it was aligned to begin with. This can result in reduced dynamic range as the sensor drifts toward one or the other of the limits of its output values. Accordingly, actual implementation of a key-type mouse employing FSR-type sensors requires some kind of automatic calibration method in order to reliably obtain sufficient dynamic range out of the sensors in order to successfully direct a cursor on a computer display.